The DSi has cameras, which means the 3DS will have to have them too if it's going to be backwards compatible. We've also heard rumors that the "next DS" will have tilt-sensors better than the iPhone. With either the camera or tilt-sensors either of these 'faux 3D' systems would work. But since we've seen the DSi do this already, it doesn't seem likely that the new hardware will rely on the same old trick.